x86: Set APs' req_seq to the reg number from device tree

Multiple APs are brought up simultaneously and they may get the same
seq num in the uclass_resolve_seq() during device_probe(). To avoid
this, set req_seq to the reg number in the device tree in advance.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>